Method of making nickel sponge cathodes



IN My y 11, 1954 J. G. BUCK 2,677,873

METHOD OF MAKING NICKEL SPONGE CATHODES Filed Jan. 10, 1946 FIG.2

INVENTOR JAMES G. BUCK ATTORNEY Patented May 11, 1954 UNITED STATES TENTOFFICE METHOD OF MAKING NI CATHODE James G. Buck, Meriden,

assignments, to the Un as represented by the This invention relatetubes, and more particu of cathodes therein.

Considerable research ha production or" cathod and with long life un sto electronic vacuum larly to the construction s been done on the eswhich will operate stably der pulsed operation in magnsmitting tubes.

pulsed performance.

One of the principal requiremen magnetron cathode is that it have goodsparking properties. Sparking can be loose1y defined as the boilin ofcathode material to the anode.

ts for a pulsed a prescribed Improvement are: (1) the impe cathodesleeve and of the coatin 3 oh the sparking may possibly be due to e of,or a combination of, the following:

electron path means drop, with a resulting discharge similar to that ofa dielectric breakdown It is questionable whether the mechanism involvedin (1) and (2) immediately above are actually difierent. In any event,concern is with the cause and not the method.

Of the several impedances it appears that. 86

N. H., assignor,

Secretary of Application January 10, 1946, Serial No.

5 Claims. (Cl.

SCKEL SPONGE by mesne of America the Navy ited States when the cathodeis sub tion, the impedance at the interface of the oathode sleeve andits coating is most important.

his interfaci jected to pulsed operaover, the heat dis ture are improvedIt is, accordingly, the object of the present invention to improve thephysical structure of cathodes.

It is another which will have good sparking properties.

her object to constr rial can be impregnated.

In the present embodiment sisting of flat flakes of nickel powder con-200 mesh size was substituted for being non-criti the nickel, cal.Similarly, inder, the ments being that it b due, and has a high 111principal requiree volatile, will leave no resielting point. r

This homogeneous mixture was pressed into a steel collar-shaped die ormold, labeled Ill on the accompanying drawings, which die is fitted ontoobject to construct a cathode supporting nickel sleeve II, this sleevebecoming part of the finished cathode structure. The metal chosen forthe sleeve is the same as that used for the mixture to avoid, amongOther things, trouble arising from different coefficients of expansion.The mixture is fired in a hydrogen furnace to volatilize the stearicacid and to sinter the flat nickel flakes together and to the nickelsleeve. Die IE is then removed to leave the sintered structure forming aporous metal collar on sleeve l I.

The sintcred structure, as seen underv a low power microscope, consistsof layers of the flat nickel flakes l2 tightly bonded together as shownin Fig. 2. The discontinuities-in. the arrangemerit of the flakes, asshown atlitof Fig. 2 are eliminated by machining the sintered structureto a desirable thickness. In the present embodiment the thickness of theporous structure after the mold was removed was approximately .020

inch, this being machined down to .010 inch in the final product.

The porous structure has a large free volume and a large interracialarea, resulting in high electrical and thermal conductivity. The use ofthe fiat nickel flakes allows for a larger interfacial area of contactbetween metal and coating. 11 similarly porous structure can be preparedby utilizing flakes which'have random shapes, and the volatile bindermay be omitted. These changes of method are made, however, at asacriflce of interfacial area;

The porous structure so prepared is impregnated with the ordinarily usedalkaline earth carbonates such as barium, calcium, or a strontiumcarbonate, the coating being-applied with a brush in the present case,and heat-treated as a conventional cathode.

In summary, the novel features, as sought to be outlined in thefollowing claims, are the construction of a porous metal sponge having alarger interracial area than the previously used screen type of cathode.The structure, there-- fore, provides for higher electrical andv thermalconductivity, with resulting sparking properties which are moredesirable for pulsed operation.

What is claimed is:

1. The method of constructing a cathode, which method includes-mixingparticles of metal with a volatile binder molding the mixture to form ahollow tube fitted onto a supporting sleeve, holding the molded mixturein contact with the sleeve while heating the mixture thereby removingthe volatile substance and sintering said particles or metal togetherand to said supporting sleeve, machining the outer surface of thecomposite structure so formed to remove discontinuities in thearrangement of particles, impregnating the composite structure soprepared with an alkaline earth carbonate, and heating untilpredetermined emission characteristics are obtained.

2. The method of constructing a base structure for a cathode, saidmethod including the steps of mixing particles of metal with amouldable, volatile binder, molding the mixture to form a molded hollowtube fitted onto a metallic sleeve, heating said mixture while supportedin intimate contact with said sleeve thereby. removing the volatilebinder and sintering said particles of metal together and to saidmetallic sleeve, and machining the outer surface of the base structureso formed to remove the outermost layer of particles.

3. The method of constructing a base structure for a cathode, saidmethod including the steps of mixing flat flakes of nickel or 100-200mesh size with stearic acid, pressing the mixture into a collar-shapedmould fitted onto the supporting sleeve to give a thickness of themixture of approximately .020 inch on said sleeve, heating said mixturewith said mould in place thereby removing the stearic acid, sinteringsaid nickel flakes together and to said supporting sleeve with saidmould in place, and machining said sintered nickel flakes with saidmould removed to leave a thickness of approximately .010 inch ofsintered flakes on said supporting sleeve.

l. The method of manufacturing a cathode comprising the steps of mixingflat flakes of metalwitha volatile binder, molding the mixture to form ahollow tube covering a metallic sleeve, supporting the molded mixture inplace while heatingthe tube and sleeve to remove the volatile binder andto sinter the metallic flakes togethcr and to said supporting sleeve,machining said composite structure to remove particles at the outersurface, and impregnating the machined structure with an electronemitting material.

5. The method of producing a porous nickel base structure for a cathodecomprising the steps of mixing flat flakes of nickel powder with stearicacid, the proportions being determined by the desired free volume in thefinal porous structure, molding the mixture to form a hollow tubecovering a nickel sleeve, supporting the molded m'ixture in place whileheating the tube and sleeve to remove the volatile binder and to sinterthe nickel flakes together and to said nickel sleeve, and machining saidcomposite structure to remove particles at the outer surface.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,051,814 Lowendahl Jan. 28, 1913 1,902,478 Wiegand Mar. 21,1933 2,172,207 Kolligs Sept. 5, 1939 2,289,658 Koehring July 14, 19422,337,588 Calkins I Dec. 28, 1943

2. THE METHOD OF CONSTRUCTING A BASE STRUCTURE FOR A CATHODE, SAIDMETHOD INCLUDING THE STEPS OF MIXING PARTICLES OF METAL WITH AMOULDABLE, VOLATILE BINDER, MOLDING THE MIXTURE TO FORM A MOLDED HOLLOWTUBE FITTED ONTO A METALLIC SLEEVE, HEATING SAID MIXTURE WHILE SUPPORTEDIN INTIMATE CONTACT WITH SAID SLEEVE THEREBY REMOVING THE VOLATILEBINDER AND SINTERING SAID PARTICLES OF METAL TOGETHER AND TO SAIDMETALLIC SLEEVE, AND MACHINING THE OUTER SURFACE OF THE BASE STRUCTURESO FORMED TO REMOVE THE OUTERMOST LAYER OF PARTICLES.